A Comprehensive Guide to Activated Carbon Filter

Activated carbon filters are used in air purifiers in order to remove pollutants from the air.  They are effective in removing volatile organic compounds (VOCs) and gaseous pollutants such as unwanted odors from closed spaces.

Activated carbon air filters capture gas molecules on a bed of charcoal.  Air cleaners generally use activated carbon filters as an additional purification method to other filters.  While they remove smells and volatile substances, these filters are not designed to remove solid particles.  This is why they make a great companion to HEPA filters.

In this article, you will learn about carbon air purifiers, how they work, their advantages, disadvantages, and whether you should use one to filter the air in your home or not.

What is an Activated Carbon Filter?

Activated carbon air filters are generally used to remove gases. Theis use allows gases to be filtered through a bed of activated carbon.  They capture volatile organic compounds (VOCs) released from many household products. They also neutralize unwanted odors from the air, such as the smell of cigarette smoke.  But how do they do that?  Let’s break them down and examine them.

What is carbon?

Carbon or charcoal are interchangeable terms.  Imagine the leftover from a burnt-out piece of wood.  The combustible material in the wood burns away, and the remaining black char is mostly carbon.  The manufacturing process of carbon is very similar to the burning of this wood piece.  A substance is heated in a vacuum chamber until it releases all volatile compounds and leaves carbon behind.  The substance is typically wood, coconut shells, coal, or other similar materials.  Each leads to slight differences in the end product.

How is carbon activated?

Carbon goes through additional processes in order to make it more effective at capturing gas molecules.  It is injected with instilled with steam, hot air, or carbon dioxide, leading it to have a porous structure and an increased surface area.  This way there are many traps for gas molecules to be captured in, and thus carbon to be used as an effective filter.  Only four grams of activated carbon translates to approximately an acre of surface area.  Activated carbon is then treated with certain chemicals in order to increase its ability to filter particular pollutants. 

As the name suggests, activated carbon filters consist almost exclusively of activated carbon in composition.  Contrary to charcoal, activated carbon has a porous inner structure.  


The two main areas where activated carbon filters can be helpful in terms of cleaning the air.

Eliminating Unwanted Odors: 

Mechanical air purifiers are good at filtering particles, however, they cannot remove unpleasant smells.  This is where activated carbon filters come to play.  They can effectively remove a good number of odor molecules such as those associated with mold or smoke.  

Filtering Volatile Organic Compounds (VOCs)

Most mechanical filters like HEPA filters cannot remove VOCs.  Carbon air filters, on the other hand, are efficient in getting rid of VOCs in the air.  They absorb and capture these substances in the filter.  These hazardous gases are commonly present in your everyday life in gasoline vapors, building materials, furniture adhesives, cigarette smoke, dry paint, or cleaning products.  

Some of the VOCs carbon filters are effective in trapping include:

  • Xylene,
  • Toluene,
  • Benzene,
  • Chlorinated compounds
  • Formaldehyde,
  • Plasticizers,
  • Certain solvents

Activated carbon filters are especially suitable for people with multiple chemical sensitivity (MCS), also known as idiopathic environmental intolerances (IEI).

Activated carbon is also a catalyst in the depletion of ozone. Thus they can be practically used in combination with ionizers, which produce ozone as a by-product.


There are certain downsides to using or only using an activated carbon filter.

Not Effective in Removing Airborne Particles:

While effective at organic compounds, activated carbon air filters cannot help with particulate pollutants, inorganic substances, and solid particles.  These pollutants include allergens such as pollen, dust, bacteria, viruses, etc.  Carbon air filters are also not able to remove wildfire or secondhand smoke.

In order to help make up for this deficiency, an air purifier may use an activated carbon filter along with a HEPA filter.

Filter Replacement:

Once the activated carbon filter is saturated with pollutants, it needs to be changed.  Replacing the carbon air filter may be time-consuming, inconvenient, and expensive.  It is also a challenge to determine when the filter needs to be changed.  We will cover this subject later on in the article.

The EPA states that gas-phase filters such as activated carbon, cannot remove carbon monoxide.

Do I Need an Activated Carbon Filter?

Perhaps you have a smoker in your home or your house went through a recent home renovation.  Or maybe you are just concerned about the VOCs released from your kitchen appliances or furniture adhesives.  If any of these are the case, an activated carbon filter air purifier is a sensible solution for you.

In any case, be aware that carbon air filters are not the most convenient or the cheapest filters to operate.  You need to monitor the saturation of the filter regularly.  You also need to replace this costly filter whenever necessary.  Furthermore, as it does not remove solid particles from your air, you may need to invest in other filters as well.  This last point can be solved by getting a hybrid air purifier that has a carbon air filter, as well as a mechanical filter like a HEPA filter. 

How to Effectively Use a Carbon Air Filter?

Carbon air filters can be effective in combatting odors and VOCs.  However, they need to be operated correctly to get the most out of them.

Enough Carbon

The amount of carbon used is essential in terms of the effectiveness of the filter.  There are activated carbon filters that only use a hint of carbon to save on costs.  These filters will almost immediately become saturated and lose effect.  Although the amount of carbon used depends on the type of carbon, size of the filter, and technology of the air cleaner, a rule of thumb amount is a minimum of five pounds of carbon.  Most of the time, it is fair to say that the more carbon is used, the better.

Correct Air Flow

The amount of time air spends passing through the filter determines the effectiveness of the cleaning.  The longer the air stays passing through the filter, the more pollutants will be successfully removed.  This time period the air passes through the filter is called ‘dwell time.’  A thick bed of concentrated carbon leads to a higher dwell time, which in turn leads to more effective filtering of the air.

Timely Filter Replacement

Once the carbon air filter is saturated, it is no longer effective.  It should then be replaced.  There is no ideal method for knowing when the carbon is saturated though.  Please follow the manufacturer’s guidelines in determining how often to replace it.  The saturation period depends on the operation time of the filter and the number of pollutants in the space it performs.  A rough guideline would be to change the carbon air filter on a monthly basis, although it is rather costly.

How Do I Clean an ACF in an Air Purifier?

Activated carbon filters are not made to be cleaned and reused.  Once the carbon air filter is saturated with particles in all its pores, it needs to be replaced.

What Types Are Available?

Different manufacturers use different substances in order to obtain activated carbon.  These may range between wood and coconut shells among other things.  However, the end product is not categorized by what substances the filter is made with. They are pretty much standard for each brand and each model.  There are other features that vary between carbon air filters.

Activated carbon filters are significantly more effective than regular carbon filters in removing air pollutants from the air.  The amount of activated carbon used in the filter also affects the outcome.  The more activated carbon a filter uses, the more pollutant particles it will catch and absorb.  A higher level of activated carbon also increases the lifetime of the filter, causing it to be replaced less often.

The size of activated carbon particles is also an important factor that varies between carbon air filters.  Smaller particles generally have a quicker absorption rate.

The most advanced activated carbon filters are infused with compounds like copper oxide and magnesium dioxide.  These compounds help remove a wider variety of hazardous pollutants from the air.  These include ethylene oxide, carbon monoxide, and ozone.  Some are even effective against the build-up of bacteria.

Make sure your replacement carbon air filter is compatible with your specific air purifier.

How Long do Activated Carbon Filters Last Before Replacement?

As mentioned earlier in the article, this may vary.  Carbon air filters get saturated after their pores are filled with air molecules.  It is rather difficult to understand exactly when they saturate.  This depends on the usage time, as well as the concentration of pollutants in the space it is used in.  

It is best to check the recommended replacement time with the manufacturer’s guidelines.  Having said that, a rule of thumb would be to replace these filters on a monthly basis.


Activated carbon filters are ideal to get rid of VOCs and unpleasant odors.  They are not effective in removing larger substances, however.  We recommend getting a hybrid air purifier that includes an activated carbon filter, as well as another mechanic filter, such as a HEPA filter.